1. Field of the Invention
This invention relates generally to a data processing system in a communications environment and more specifically to the use of two microprocessors, one for communicating with the devices and the other for communicating with the central processor unit and main memory.
2. Description of the Prior Art
Data processing systems are coupled to a multiplicity of communication lines by a communication controller or as it is commonly called a communication multiplexer. Each of the communication lines may be coupled to a device, typically a cathode ray tube display (CRT). The communication controller is operative to transfer data between a main memory of the data processing system and the devices via the communication line.
Prior art communication multiplexers such as described in U.S. Pat. No. 3,500,466 entitled "Communication Multiplexing Apparatus" includes a first processor for effecting the assembling of data bits from a plurality of communication lines and a second processor for effecting the transfer of data characters between the first and the data processor subsequent to the receipt of one or more special control characters. This had the problem of limiting the throughput and requiring extensive hardware, since the single bit processor was required to assemble the bits into bytes by comparing the bits received from each line with a special stored character.
The hardware required is reduced by the use of a microprocessor controlling communication lines through the use of channel control blocks stored in a memory. Such a system is described in U.S. Pat. No. 4,133,030 entitled "Control System Providing for the Transfer of Data in a Communications Processing System Employing Channel Dedicated Control Blocks". This system, however, limited the throughput by restricting the number of communication lines that could be processed.
It should be understood that the references cited herein are those which the Applicants are aware of and are presented to acquaint the reader with the level of skill in the art and may not be the closest reference to the invention. No representation is made that any search has been conducted by the Applicants.